1. Field of the Invention
The present invention relates generally to a broadcasting service using an optical transmission network, and in particular, to a broadcasting service using an ATM (Asynchronous Transfer Mode) optical transmission network.
2. Description of the Related Art
Conventional digital broadcasting services may deliver broadcast data to a plurality of subscribers using an optical transmission network.
A conventional analog broadcasting service delivers all the channel data to a subscriber, and the subscriber then selects a desired channel through a TV receiver or a set-top box to receive a broadcasting service. However, unlike the analog broadcasting service, the digital broadcasting service cannot transmit all the channel information to the subscriber so that he or she can select a desired channel. This is because in the digital broadcasting service, each channel is required to be transmitted at about 20 Mbps for HD (High Definition) TV and at about 3 to 6 Mbps even for SD (Standard Definition) TV. Therefore, as the number of the channels is increased, the transmission to the subscriber would require a rate of several hundreds or higher of Mbps. Therefore, it is not practical or possible to deliver all the channel information to the subscriber.
Accordingly, the digital broadcasting service receives channel information desired by a subscriber from an optical line terminal (OLT) or an optical network unit (ONU) and transmits only his or her desired channel data to the subscriber.
In this arrangement, switching between a digital broadcast channel and a subscriber for connecting the digital broadcast channel to the subscriber becomes important.
FIG. 1 illustrates a block diagram of a conventional optical transmission network for a digital broadcasting service. As illustrated in FIG. 1, the conventional optical transmission network includes an optical line terminal (OLT) 11 for electro-optic converting digital broadcast data provided from a broadcasting service provider. The converted digital broadcast data are grouped into one optical signal to provide a digital broadcasting service to a subscriber 13. An optical network unit (ONU) 12 is used to deliver information from the OLT 11 to the subscriber 13. An optical cable connects the OLT 11 to the ONU 12.
The ONU 12 includes an SDH (Synchronous Digital Hierarchy)-to-ATM processor 103 for converting an optical signal including digital broadcast data received from the OLT 11 into an electric signal in an ATM format, an ATM cell classifier 104 for classifying digital broadcast data according to channels, a broadcast channel information processor 101 for processing broadcast channel information provided from the OLT 11, a controller 102 for controlling each element, and a switch 105 for switching the classified digital broadcast data of each channel to each subscriber.
In operation, each of several broadcasting service providers transmits digital broadcast data to the OLT 11 via each virtual channel connection (VCC). The VCC refers to a communication channel on a virtual path (VP) which is a path obtained by grouping several strands of channels into a sheaf. The OLT 11 converts the digital broadcast data into SDH-formatted optical signal, and transmits the SDH-formatted optical signal to the ONU 12. In the ONU 12, the SDH-to-ATM processor 103 converts the SDH-formatted digital broadcast data transmitted by the OLT 11 into an ATM-formatted digital broadcast data. The ATM-formatted digital broadcast data is classified by the ATM cell classifier 104 into digital broadcast data from each channel. The digital broadcast data from each channel is applied to the switch 105 and then switched to the subscriber 13 at the request of the subscriber 13. The digital broadcast data classified into ATM cell does not include broadcast channel information for corresponding digital broadcasting, and a broadcast channel information processor 101 is included to process such broadcast channel information.
The broadcast channel information is delivered from the OLT 11 through a separate line. The broadcast channel information delivered to the broadcast channel information processor 101 also includes broadcasting station information corresponding to a program ID (PID) contained in digital broadcast data. In this manner, it is possible to update a channel that is added, changed and deleted optionally by the OLT 11 or the broadcasting service provider.
However, the conventional method has the following two problems.
First, an increase in the number of digital broadcast channels increases the number of output channels of the ATM cell classifier 104 that classifies digital broadcast data according to broadcast channels. This means that the switch 105 must switch the increased number of channels. In general, a high-capacity switch having a large number of inputs and outputs is complicated in operation and expensive in cost. In addition, if the number of channels is increased beyond the available capacity of the switch 105, the switch 105 must be replaced with a new one, causing a service problem.
Second, in the conventional optical transmission network for digital broadcasting, each ONU has PID information for digital broadcast data of each channel through Ethernet, and the changed digital broadcast channel information is artificially updated from the OLT 11 to the ONU 12 during addition or deletion of a digital broadcast channel and rearrangement of a broadcast channel. However, during addition of a new digital broadcast channel or deletion of an existing digital broadcast channel and/or rearrangement of a broadcast channel, the changed digital broadcast channel information is artificially provided from the OLT 11 to the ONU 12. Thus, during addition of a new digital broadcast channel or deletion of an existing digital broadcast channel and/or rearrangement of a broadcast channel, the subscriber 13 may fail to receive information about the change unless the information is artificially updated to the ONU 12. In addition, the broadcast channel information is transmitted through a separate line, requiring additional hardware (e.g., line).